This invention relates to a portable, engine driven generators, and more particularly to a portable generator which automatically adapts itself to parallel operation of three or more portable generators connected in parallel with each other by automatically synchronizing the phases of outputs of the generators.
Because of manufacturing and operational inconsistencies, each portable, engine driven generator produces electricity at a slightly different voltage and frequency and with a different phase between the voltage and current. When two or more portable generators are connected in parallel with each other in operation, then if the phases or amplitudes of the output voltages from the generators are not synchronous, it will causes electric current to flow from one generator into another generator, which can result in the damage of component parts of one or more of the generators. Therefore, it is desirable to synchronize the phases and amplitudes of the output voltages from each of the joined generators.
To this end, even in the case of parallel operation of identically-constructed portable generators, the prior art has provided ways to try and synchronize generators. For example, U.S. Pat. No. 5,258,700 generates a target output sine waveform with a frequency based on phase differences among the joined generators and uses the switching control of the inverters adjust each generator's output to match the target signal. This patent also refers to Japanese Patent Publication (Kokoku) No. 56-20782 which uses an automatic synchronizing device and means for producing an operating point at which the electrical phases of two plural generators coincide with each other in order to cause the automatic synchronizing device to operate promptly and reliably. U.S. Pat. No. 5,258,700 also refers to Japanese Provisional Utility Model Publication (Kokai) No. 62-145440 uses a special adaptor for parallel operation of two portable generators, with one of them serving as a master generator while the other serves as a slave generator.